Our long-term goal is to determine and quantitate factors that predispose cerebral circulation to stroke. In the brain, essential hypertension is compensated by chronic vasoconstriction, cerebral blood flow is autoregulated within a narrow range and cerebral perfusion is under threat during conditions, which increase metabolic demands. Because transient ischemic attacks (TIAs) often herald stroke, we plan to use state-of-the-art noninvasive tools to determine if impaired cerebral autoregulation predisposes to stroke in hypertensive patients with and without TIAs. We will examine cerebral vasoregulation from blood flow velocity of middle cerebral artery (MCA) using transcranial Doppler (TCD) in hypertensive patients with and without TIAs and their responses to orthostasis, rapid changes of blood pressure and hypocapnia and hypercapnia.